The invention relates to a method for controlling an internal combustion engine with interventions in at least one manipulated variable.
In the context of controlling internal combustion engines it is known to determine a setpoint torque which is to be generated by the internal combustion engine. Various manipulated variables of the internal combustion engine can be set in combination in such a way that the setpoint torque is generated in the steady-state condition.
In this context, reference is made, as prior art, by way of example to DE 198 03 387 C1 from which it is known to assign priorities to various torque requirements in such a way that ultimately a setpoint torque is determined which is then to be set. These various torque requirements relate, on one hand, to a desired torque determined by the driver of the vehicle and to setpoint torques which are predefined by subsystems. These subsystems can be, for example, a control for controlling distances from other vehicles, a cruise control, a controller for vehicle movement dynamics and/or a transmission controller.
DE 198 07 124 A1 discloses how a standard interface is provided to the effect that a setpoint for the internal combustion engine is predefined centrally. Furthermore, various procedures are described in said document which describe interventions in manipulated variables of the internal combustion engine during which the setpoint torque can be set with different speeds. For example, a setting of the setpoint torque which is optimized with respect to the efficiency of the internal combustion engine is made by setting the load. Furthermore, alternatively or additionally the ignition angle can be adjusted if, for example, the setpoint torque is to be set quickly.
DE 43 15 885 C1 and DE 196 15 542 C2 disclose various procedures for generating torques which are determined by defined interventions in the manipulated variables of the internal combustion engine.
It is the object of the present invention to provide a method of controlling an internal combustion engine by which the torque to be generated by the internal combustion engine can be set as precisely as possible.
In a method for controlling an internal combustion engine by means of interventions in at least one manipulated variable of the internal combustion engine, a setpoint torque or work which is to be performed is determined at the crankshaft of the internal combustion engine, wherein, with respect to a first variable as work which is to be performed or a setpoint torque to be provided, a corresponding setpoint quantity of heat is determined taking into account the instantaneous actual efficiency, with respect to which at least one associated manipulated variable is set in accordance with the value of the set-point quantity of heat, and, for precise setting of the torque, the actual quantity of heat also being sensed, a setpoint efficiency being determined from the actual quantity of heat taking into account work which is to be performed or a setpoint torque which is to be provided, this can correspond to the first variable or to another variable which is formed as a setpoint torque or work which is to be performed at the crankshaft, and at least one manipulated variable of the internal combustion engine is set approximately simultaneously in accordance with a setting of the setpoint efficiency.
When controlling the internal combustion engine, it is not necessary to provide an absolutely precise setting of the torque under all operating conditions. Instead, by using the method according to the invention, it is possible to perform an exact setting under certain operating conditions under which a predefined torque is to be set in a precise way. This relates, for example, to torque values required by safety-critical systems such as a traction controller or operating conditions such as torque switching. It is then possible to provide a rapid and precise setting of the correct torque by intervening in at least one manipulated variable which influences the efficiency. In a direct-injection engine or a diesel engine, such a rapid and precise setting of the torque can also be performed by means of the supplied quantity of heat in the form of the amount of fuel supplied. If a torque which has been defined by the driver is to be set, it is also possible to tolerate deviations within certain limits so that during the control an optimum efficiency can then be set in order to optimize emissions and/or save fuel.
The manipulated variable may be set in the next working cycle or, if appropriate, even in the current working cycle.
The procedure is therefore based, during the precise setting of the torque, on determining, in one working cycle, the work which is to be performed at the crankshaft (the setpoint torque). The setpoint quantity of heat for this working cycle is determined in accordance with the current efficiency which results from the setting of the manipulated variables of the internal combustion engine in this working cycle. This setpoint quantity of heat can be set by means of corresponding manipulated variables such as the volumetric efficiency (during homogeneous operation in a spark ignition engine) or the quantity of fuel injected (in stratified charge mode, in a diesel engine or a spark ignition engine). Furthermore, the actual quantity of heat is sensed. As a result, a possible deviation can be detected.
Settings of manipulated variables which influence the efficiency are then obtained by virtue of the fact that a setpoint efficiency is determined from the actual quantity of heat and from the work which is to be performed. This setpoint efficiency can then be set approximately simultaneously by means of a manipulated variable or an interaction between a plurality of manipulated variables. For example, the ignition time can be adjusted in order to limit the efficiency, or the valve control can be varied. It is also possible here to initiate an intervention in the manipulated variables with an intervention in the setting of the ignition time because this manipulated variable can be influenced on a short-term basis. The intervention in this manipulated variable can then be combined with an intervention in the valve control. The setting of the valve control cannot be influenced in such a short-term fashion as the setting of the ignition time. A combined intervention can, for example, give the appearance that interventions have been carried out both in the setting of the ignition time and in the setting of the valve control. As the influence of the intervention in the valve control increases, the adjustment of the ignition time can be reversed when the intervention in the valve control appears to take effect, taking into account the system setting times.
The first variable can in turn be used in the calculation of the setpoint efficiency, as it is explained, for example, below in conjunction with the switching of operating modes such as, for example, a cylinder shut off or a change from stratified charge mode into homogeneous mode in a direct-injection spark ignition engine. However, a different variable can also be used, which is likewise determined as the setpoint torque or work which is to be performed at the crankshaft, as is explained, for example, below in conjunction with the setting of a reserve torque in which the setpoint quantity of the heat, which is set is increased in comparison with the setpoint torque, which is to be set at a given time, and is xe2x80x9ccorrectedxe2x80x9d by means of a corresponding setting of the efficiency, in order to obtain a better setting speed when a relatively large torque change is desired.
The work which is to be performed at the crankshaft can be determined taking into account various influencing factors. It is possible, for example, to take into account torque requirements of assemblies of the internal combustion engine. Furthermore, inert masses of the internal combustion engine itself can also be taken into account. Furthermore, the driver""s request with respect to a possible acceleration or deceleration is also included. Further requirements, which are predefined, for example, by the control of an automatic gearbox, by a traction controller, by a controller for vehicle movement dynamics etc., can be superimposed on this driver""s request.
As has already been described, it is also possible to perform a precise setting of the torque by setting manipulated variables which influence the efficiency only if the operating mode or the combustion method is to be switched or if a torque value required by a safety-control system, such as a traction controller or a controller for vehicle movement dynamics, has been defined.
In this control, guide variables which can be determined on each internal combustion engine irrespective of its operating mode are advantageously used. These are in this case the quantity of heat, in which case one or more further manipulated variables which influence the efficiency and can thus lead to a rapid setting of a precise torque are present. It is therefore in particular not necessary to provide different control methods as a function of operating modes or internal combustion engines used. Instead, it is possible to integrate various internal combustion engines in various operating modes into this control in a modular fashion. As a result, it is also possible to avoid problems which relate to jumps in torque if, for example, different operating methods have to be used in different operating modes and said operating methods possibly lead to instabilities in the transition range.
If the intake work of the cylinder in the intake period in the respective working cycle, the compression work of the cylinder in the compression period in the respective working cycle, the combustion work of the cylinder in the combustion period in the respective working cycle and the expulsion work of the cylinder in the expulsion period in the respective working cycle are taken into account in the respective working cycle during the determination of the work to be performed at the crankshaft, the work performed at the crankshaft can be determined even under unsteady-state conditions in synchronism with the working cycle. An exemplary embodiment of the implementation is explained in conjunction with the figures.
Also, a control error of the induced torque at the crank-shaft may be derived from a deviation of the rotational speed of the crankshaft from a setpoint rotational speed, this control error being taken into account in the determination of the setpoint torque or the work which is to be performed at the crankshaft.
This configuration advantageously provides the possibility of providing a central comfort manager with which jumps in the rotational speed and a jolting driving characteristic brought about by this can be compensated as quickly as possible, it is possible to intervene in manipulated variables of the internal combustion engine approximately simultaneously, with an appropriate correction.
It is possible to draw conclusions as to the necessary change in the induced torque from the inertia moment from an energy balance of the rotation energy. The control comfort can be significantly improved by appropriately taking into account this variable.
When it is necessary to change the intake manifold pressure during ongoing operation of the internal combustion engine, the change in the setting of the throttle valve is increased by a precise absolute value and for such a period of time that the increase in the setting of the throttle valve corresponds approximately to the air mass flow rate which is required to set the internal combustion engine to the new load state.
It proves advantageous here that the setting of the new load state takes place significantly more quickly by virtue of the fact that the increased actuation of the throttle valve shortens the transient response to the new load state. This takes place because, the throttle valve is opened further in the time period of the transition than corresponds to the new load state when there is a transition to a state with a relatively large load.
This can be carried out, for example, by using a model, which places the intake manifold pressure, the temperature and the volume in relationship with the masses of the gases, is used to estimate, by reference to the ideal gas equation, which change in the mass over time is required for a specific change in the intake manifold pressure over time. In accordance with this change in the mass over time, it is then possible to calculate which adjustment of the throttle valve is necessary.
The dynamics during the setting of changing load states of the internal combustion engine are therefore advantageously improved by the use of the present invention.
The method can, for example, be used in an internal combustion engine with cylinders which can be shut off. During the shutting off of the cylinders, the gas exchange is prevented because the input and output valves are not actuated. When the cylinders which can be shut off are returned to operation, i.e. at the resumption of the actuation of the input and output valves, it is possible to set rapidly the new load states using the present invention.
When it is necessary to change the intake manifold pressure during ongoing operation of the internal combustion engine, a time profile of the throttle valve setting is determined in such a way that the new intake manifold pressure is set in a way which is optimized with respect to time on the basis of the time profile of the mass flow rate which is set as a result of the throttle valve setting.
The time profile of the throttle valve setting can advantageously be determined in such a way that the mass flow rate resulting from the extreme settings of the throttle valve (opened or closed to a maximum extent) is determined on the basis of said extreme settings. As already pointed out, it is also possible to determine from the air mass flow rate demand, which is required, for example, in the case of a relatively large load, and from the resulting mass flow rate, the period of time in which the throttle valve has to be opened to a maximum extent in order to obtain the change in the load state of the internal combustion engine in an optimal way with respect to time. The throttle valve is then actuated in such a way that, at the start of the transition to the state with a larger load, the throttle valve is opened to a maximum extent for the specific period of time. The throttle valve is then set to the value which corresponds to the required mass flow rate for the new load state in steady-state operational mode. The actuation of the throttle valve is then carried out by means of a jump function. Analogously, when the internal combustion engine is to be set, to provide a low load the period of time for which the throttle valve has to be closed can be determined so as to obtain the optimal state for a relatively low load of the internal combustion engine. It is however necessary to retain an air mass flow. The time period can be obtained by determining the mass flow rate at a throttle valve setting which corresponds to the new load state. The time period during which the throttle valve has to be closed is obtained on the basis of the air mass to be retained and the mass flow rate which is determined.
A particularly rapid setting of changed load states can advantageously be brought about by means of this configuration of the method.
In a particular embodiment of the method according to the invention, a time profile of the anticipated value of the mass flow rate which is set or of the intake manifold pressure which is set is determined on the basis of the time profile of the throttle valve setting, the actual value of the mass flow rate or of the intake manifold pressure is determined, and when there is a deviation of the actual value from the associated anticipated value, the throttle valve is actuated in order to eliminate the deviation.
As a result, it is possible to sense by means of a control, whether the desired time profile of the intake manifold pressure or the mass volumetric efficiency is set on the basis of the actuation of the throttle valve. If this is not the case, the manipulated variable (setting of the throttle valve) can be correspondingly changed. If the throttle valve is already actuated to a maximum extent, i.e. either entirely opened or entirely closed, it is possible, for example, to correspondingly correct the time period during which this maximum actuation of the throttle valve takes place. As a result, the setting precision during a dynamically rapidly occurring change in the load state is improved further. The corresponding variables can either be measured directly or derived on the basis of a model by reference to other measurement variables.
It is possible that individual cylinders of the internal combustion engine are shut off in that, in a first step, it is tested whether the calculated mass volumetric efficiency can be set appropriately for operation with a reduced number of cylinders. In a further step, a throttle valve is actuated in such a way that the intake manifold pressure corresponds to the mass volumetric efficiency with a reduced number of cylinders. During this step, the torque at the crankshaft is set in a fashion synchronized from one working cycle to the next by an intervention in manipulated variables which influence the efficiency, the cylinders being shut off when the corresponding intake manifold pressure is reached.
As a result, it is possible for the torque-generating parameters to be switched without jumps in the torque. During the intervention in the ignition or the quantity of fuel injected, this intervention can take place in such a way that exhaust gas regulations are complied with. Here, it is possible, for example, to actuate individual cylinders differently in order to obtain better exhaust gas values in a mixed mode than when the cylinders are actuated uniformly. The jump in the torque can be avoided by setting that the intake manifold pressure, which can be set only with a certain degree of inertia, to the new value before the switching operation. During this setting of the intake manifold pressure to the new value, the torque can be set by the intervention in the manipulated variables which influence the efficiency, for example, the ignition and/or the quantity of fuel, with the result that an undesired jump in the torque does not occur because the mass volumetric efficiency has already approached the conditions which are adapted to the time after the switching operation, while the internal combustion engine is still operated with the full number of cylinders. As a result of the intervention in the manipulated variables which influence the efficiency, it is possible to adapt torque flexibly in a synchronized fashion from one working cycle to the next with rapidly set-table manipulated variables with short time constants.
The setting of the throttle value can advantageously be carried out so that the switching process can again be shortened by the new intake manifold pressure which is set more rapidly. A rotational speed correction can also be carried out as mentioned earlier.
Cylinders, which have been shut off, are connected by virtue of the fact that the throttle valve is actuated in such a way that the intake manifold pressure corresponds to the mass volumetric efficiency with the full number of cylinders. The cylinders, which have been shut off, are connected simultaneously and the torque at the crankshaft is set in a synchronized fashion from one working cycle to the next at the crankshaft by means of an intervention in manipulated variables which influence the efficiency.
This method corresponds to the inverse conditions. Here, the mass volumetric efficiency is adapted before the switching operation to the operation with a reduced number of cylinders so that an increased torque is produced during the switching to the operation with a full number of cylinders. This torque can in turn be reduced in a synchronized fashion from one working cycle to the next in that an intervention is made in the manipulated variables which influence the efficiency, for example therefore an intervention in the ignition and/or the quantity of fuel, with the result that no jump in the torque occurs in the switching phase. This switching phase lasts until the intake manifold pressure is set to the mass volumetric efficiency with a full number of cylinders by a corresponding setting of the throttle valve.
If appropriate, when shut-off cylinders are switched on again, it is also possible to take into account deviations in the mass volumetric efficiency of the shut-off cylinders owing to the lack of gas dynamics in the intake manifold when they are switched on again. Likewise, differences in the indexed high-pressure efficiency at the transition can be taken into account.
If the internal combustion engine is a direct-injection spark ignition engine for switching over from the stratified charge into the homogeneous mode, and vice versa, at least one pattern is stored in a control unit in which the torques which are to be set in each working cycle during the switching process are stored, and in which case the switching time is defined by reference to the torques in the respective pattern which are to be set, in such a way that the torques can be set during the switching process by means of permitted interventions in manipulated variables which influence the efficiency.
During a switching operation of a direct-injection spark ignition engine from the stratified charge mode into the homogenous mode, and vice-versa, the corresponding change in the compression and expansion work during the determination of the intervention in the manipulated variables with the aim of achieving a constant torque is taken into account in each working cycle at the change-over of the operating mode. It is checked, by reference to the prevailing conditions and the stored patterns for switching processes, when the switching point is to be selected so that intervention in the manipulated variables of the internal combustion engine occurs only in a permissible fashion. The permissibility of this intervention in the manipulated variables of the internal combustion engine can be defined, for example, in such a way that reliable engine operation has to be ensured. Furthermore, interventions which lead to unacceptable gas values can be avoided. In this method, a jump in the torque is therefore primarily avoided. In addition to avoiding this jump in the torque, further criteria can be taken into. The manipulated variables which influence the efficiency can, for example, be again the ignition time and/or the quantity of fuel.
An exemplary embodiment of the invention will be described below on the basis of the accompanying drawings.